Apparatus and method for transmitting/receiving data in a CDMA mobile communication system

ABSTRACT

A data transmitting/receiving apparatus and method for improving the reliability of data bits in a CDMA mobile communication system. High-priority bits are mapped to a high-reliability bit position and low-priority bits, to a low-reliability bit position in symbols. Thus system performance is improved at a transmission.

PRIORITY

[0001] This application claims priority to an application entitled“Apparatus and Method for Transmitting/Receiving Data in a CDMA MobileCommunication System” filed in the Korean Industrial Property Office onOct. 29, 2001 and assigned Serial No. 2001-66887, the contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to an apparatus andmethod for transmitting/receiving data in a CDMA (Code Division MultipleAccess) mobile communication system, and in particular, to an apparatusand method for transmitting/receiving data with an increasedreliability.

[0004] 2. Description of the Related Art

[0005] It is impossible in practice to receive pure signals withoutsignal distortion or noise. The influence of distortion or noise is moresevere in a wired network than in a wireless network.

[0006] Accordingly, great amounts of time and energy have been expendedtoward minimizing the influence of distortion or noise involved withsignal transmission and reception in a mobile communication system. Themajor method of reducing the effects of distortion and noise is througherror control coding. Codes used for the error control coding aredivided into memoryless codes and memory codes. The memoryless codesinclude a linear block code. The memory codes include a convolutionalcode and a turbo code. A channel encoder generates the code to includesystematic bits and parity bits according to an error control codingtechnique. The turbo code is generally used for the error controlcoding. A systematic convolutional code also has systematic bits andparity bits.

[0007] The systematic bits are information bits transmitted from atransmitter to a receiver, and the parity bits are added at channelencoding to correct at decoding errors generated during transmission ofthe systematic bits. Even for an error control coded signal, bursterrors in systematic bits or parity bits are difficult to correct for.The burst errors, which are often generated on a fading channel, can beprevented by interleaving. Interleaving is performed to distribute datahaving the same information to overcome the shortcoming of the errorcontrol coding.

[0008] An interleaved signal is mapped on a symbol basis in a digitalmodulator. The symbol mapping refers to designation of symbol positionsin a two-dimensional plane (a symbol constellation) having an I channelalong an X axis and a Q channel along a Y axis. It is determinedaccording to a modulation scheme such as QPSK (Quadrature Phase ShiftKeying), 8PSK, 16QAM (Quadrature Amplitude Modulation) and 64QAM. Thesymbol mapping is performed according to the number of bits in amodulation symbol and the values of the bits. The number of bits in amodulation symbol depends on a modulation scheme as listed in Table 1.TABLE 1 Modulation Number of bits mapped QPSK 2 8PSK 3 16QAM 4 64QAM 6

[0009] Referring to Table 1, the number of bits in a modulation symbolincreases as a modulation order increases. For example, one modulationsymbol includes at least four bits in a modulation scheme having amodulation order equal to or greater than that of 16QAM. Bits are mappedto a modulation symbol in the symbol constellation.

[0010] Transmission reliability and symbol mapping according tomodulation schemes will be described with reference to FIGS. 1, 2 and 3.

[0011] As illustrated in Table 1, one symbol in a general modulationscheme contains a plurality of coded bits and is represented by a pointin a symbol constellation. The symbol constellation is divided into fourmacro regions (hereinafter, four quadrants), left, right, up and downaccording to positions along the X axis (I channel) and the Y axis (Qchannel). Micro regions, namely, demodulation regions, are defined ineach quadrant. Part of coded bits in a modulation symbol designate oneof the four quadrants and the other coded bits designate a demodulationregion or specific coordinates in the designated quadrant. The formercoded bits are referred to as quadrant determining bits, and the lattercoded bits are referred to as demodulation determining bits. Both I andQ channel values are positive in the first quadrant, I channel valuesare negative and Q channel values are positive in the second quadrant,both I and Q channel values are negative in the third quadrant, and Ichannel values are positive and Q channel values are negative in thefourth quadrant. The demodulation regions can be further dividedaccording to other modulation schemes used.

[0012] During symbol transmission on a radio channel, most errors occurin demodulation regions in the same quadrant. Thus the error probabilityof quadrant determining bits is higher than that of demodulationdetermining bits. In other words, the quadrant determining bits have arelatively high reliability, whereas the demodulation determining bitshave a relatively low reliability. In a modulation symbol, macro regiondetermining bits are referred to as high-reliability bits, micro regiondetermining bits are referred to as low-reliability bits, and anyremaining bits are referred to as medium-reliability bits. These are bitreliabilities in the symbol.

[0013]FIGS. 1, 2 and 3 are diagrams illustrating symbol constellationsrepresenting the bit reliabilities of a symbol in 8PSK, 16QAM, and64QAM, respectively.

[0014] Referring to FIG. 1, one modulation symbol contains three codedbits in 8PSK. The three coded bits determine the position of the symbolin the symbol constellation. Specifically, the first two bits indicateone of the four quadrants, and the remaining one bit indicates a point(coordinates) in the quadrant. For example, if a symbol has coded bits“011”, the quadrant determining bits “01” indicates the second quadrantand the demodulation determining bit “1” indicates a specific mappingpoint in the second quadrant.

[0015] Referring to FIG. 2, one modulation symbol occupies four codedbits in 16QAM. The first two quadrant determining bits indicate one ofthe four quadrants and the other two demodulation determining bitsindicate a particular demodulation region in the quadrant. In FIG. 2,four demodulation regions are defined in each quadrant. For example,coded bits “1011” are mapped to a particular symbol indicated by thedemodulation determining bits “11” in the second quadrant indicated bythe quadrant determining bits “10”.

[0016] Referring to FIG. 3, one modulation symbol contains six codedbits in 64QAM. The first two quadrant determining bits indicate one ofthe four quadrants and the other four demodulation determining bitsindicate a particular demodulation region in the quadrant. In the 64QAMsymbol constellation, four main demodulation regions are defined in eachquadrant and four sub-demodulation regions are defined in each maindemodulation region. For example, coded bits “101111” are mapped to anupper left symbol indicated by the sub-demodulation determining bits“11” in the upper left main demodulation determining bits “11” in thesecond quadrant indicated by the quadrant determining bits “10”. In FIG.3, the main demodulation regions are marked with bold dotted lines andthe sub-demodulation regions are marked with slender dotted lines.

[0017] Table 2 below illustrates symbol reliability patterns for 8PSK,16QAM, 10 and 64QAM. TABLE 2 Modulation Symbol reliability pattern 8PSK[H, H, L] 16QAM [H, H, L, L] 64QAM [H, H, M, M, L, L]

[0018] In Table 2, H denotes a high reliability, M denotes a mediumreliability, and L denotes a low reliability.

[0019]FIG. 4 is a block diagram of a transmitter in a typical HSDPA(High Speed Downlink Packet Access) mobile communication system.Referring to FIG. 4, the transmitter includes a channel encoder 430, aninterleaver 440, and a modulator 450.

[0020] Upon input of N transport blocks from a data source 410, a CRCadder 420 adds CRC bits to each transport block. The channel encoder 430encodes the CRC-attached N transport blocks at a code rate, for example,½ or ¾. If the channel encoder 430 supports a plurality of coded ratesthrough symbol puncturing or repetition with a mother code rate of ⅙ or⅕, an operation for selecting one of the code rates is required. In thetransmitter, the channel encoder 430 determines its code rate under thecontrol of a controller 460.

[0021] While a rate matcher is not illustrated in FIGS. 4, 5 and 6, ifrequired, it can be disposed between the channel encoder 430 and theinterleaver 440. In this case, the rate matcher matches the data rate ofthe coded bits by repetition and puncturing when transportchannel-multiplexing is needed, or if the number of the coded bits isdifferent from that of bits to be transmitted through the air. Theoperation of the rate matcher will not be described hereinafter.

[0022] To minimize data loss caused by burst errors, the interleaver 440interleaves the coded bits. The modulator 450 maps the interleaved bitsto symbols in a modulation scheme determined by the controller 460. Thecontroller 460 selects the code rate and the modulation scheme accordingto the current radio channel condition. To selectively use QPSK, 8PSK,16QAM, and 64QAM according to the radio environment, the controller 460supports AMCS (Adaptive Modulation and Coding). Though not shown,transmission data is spread with a Walsh code for channelization andspread with a PN (Pseudorandom Noise) code for identifying a BS.

[0023] The output of the channel encoder 430 is divided into systematicbits and parity bits that differ in priority. When transmission data hasa particular error rate, it is better for decoding at a receiver to haveerrors in the parity bits than in the systematic bits because thesystematic bits are real data and the parity bits are added for errorcorrection at decoding, as described before.

[0024] Therefore there is a need for dealing with systematic bits andparity bits discriminately according to their priority levels in symbolmapping. To meet the need, SMP (Symbol Mapping based on Priority) isdiscussed for HSDPA (High Speed Downlinks Packet Access)standardization. SMP is a technique of combining the priorities of codedbits with reliabilities in a symbol. By SMP, high-priority coded bitsand low-priority coded bits are mapped to high-reliability bit locationsand low-priority bit locations, respectively in symbol mapping in orderto reduce the probability of generating errors in relatively significantbits and thus improve reception performance.

[0025]FIG. 5 is a block diagram of a transmitter in a conventional HSDPAmobile communication system supporting SMP. The transmitter ischaracterized by mapping high-priority systematic bits tohigh-reliability bit locations in a symbol.

[0026] Referring to FIG. 5, a channel encoder 530 separately outputssystematic bits and parity bits. A first interleaver 540 and a secondinterleaver 550 separately interleave the systematic and parity bits.The first and second interleavers 540 and 550 are physically orlogically separated to allow the coded bits to be mapped to symbolsaccording to their priority levels. A PSC (Parallel-to-Serial Converter)560 converts the interleaved systematic and parity bits to a serial bitstream according to the modulation scheme of a modulator 570 and thecode rate of the channel encoder 530 under the control of a controller580, taking into consideration that the number of systematic bits andparity bits change according to the code rate. The modulator 570 mapsthe serial bits to symbols. The symbols have a reliability pattern [H,H, L] in 8PSK, [H, H, L, L] in 16QAM, and [H, H, M, M, L, L] in 64QAM.Also shown are data source 510 and CRC adder 520.

[0027] Implementation of SMP in 16QAM will be described below.

[0028] When the code rate is ½ and the modulation scheme is 16QAM, thechannel encoder 530 outputs systematic bits and parity bits which areequal in number, and each modulation symbol output from the modulator570 has a reliability pattern [H, H, L, L]. Thus two systematic bits aremapped to a high reliability part (H), and two parity bits are mapped toa low reliability part (L). When the code rate is ¾ and the modulationscheme is 16QAM, the channel encoder 530 outputs systematic bits andparity bits at a ratio of 3:1, and each modulation symbol output fromthe modulator 570 has a reliability pattern [H, H, L, L]. Thus two ofthree systematic bits are mapped to a high reliability part (H), and onesystematic bits and one parity bit are mapped to a low reliability part(L).

[0029] The SMP technique implemented in the transmitter illustrated inFIG. 5 is disclosed in Korea Patent Application No. 2001-17925 filed bythe present applicant, the contents of which are incorporated herein byreference.

[0030]FIG. 6 is a block diagram of a transmitter in a conventional HSDPAmobile communication system supporting CoRe (ConstellationRearrangement).

[0031] The CoRe technique is an advanced retransmission method underdiscussion, in which the reliabilities of bits in each symbol areaveraged by rearranging a high-order modulation constellation at aretransmission. To achieve the purpose of the CoRe technique, thetransmitter illustrated in FIG. 6 further includes a rearrangementcontroller 670. The same components as in the transmitter illustrated inFIG. 4 will not be described.

[0032] Referring to FIG. 6, the rearrangement controller 670 providesoverall control in cooperation with a controller 660 to rearrangepreviously coded bits upon request for a retransmission from a receiver.A modulator 650 maps interleaved coded bits to symbols in aconstellation which can be changed according to the number oftransmission occurrences.

[0033]FIGS. 7A to 7D illustrate examples of constellations for initialtransmission and retransmissions. Specifically, FIG. 7A illustrates aconstellation for an initial transmission, FIG. 7B illustrates aconstellation for a first retransmission, FIG. 7C illustrates aconstellation for a second retransmission, and FIG. 7D illustrates aconstellation for a third retransmission. For a fourth retransmissionand afterwards, the constellations illustrated in FIGS. 7A to 7D arerepeatedly used in sequence.

[0034] For example, coded bits “0011” are mapped to the upper rightsymbol in the first quadrant at an initial transmission as illustratedin FIG. 7A, then mapped to the lower left symbol in the third quadrantat a first retransmission as illustrated in FIG. 7B, then mapped to thelower left symbol in the first quadrant at a second retransmission asillustrated in FIG. 7C, and then mapped to the upper right symbol in thethird quadrant at a third retransmission as illustrated in FIG. 7D. Thefirst two bits “00” of the coded bits “0011” assumes high reliability(H) in the first quadrant at the initial transmission. “11” arehigh-reliability bits in the third quadrant at the first retransmission,“00” are high-reliability bits in the first quadrant at the secondretransmission, and “11” are high-reliability bits in the third quadrantat the third retransmission. This constellation rearrangement effectsaveraging the reliabilities of the coded bits. While the constellationsillustrated in FIGS. 7A to 7D are defined to 16QAM, the sameconstellation rearrangement may occur in all high-order modulations.

[0035] The SMP matches priority to reliability, and the CoRe averagesreliabilities irrespective of priority. Yet the two techniques commonlyutilize bits with different reliabilities within a symbol.

[0036] However, the SMP and CoRe techniques cannot coexist becausesymbol mapping irrespective of priority discords with priority-basedprocessing of coded its.

SUMMARY OF THE INVENTION

[0037] It is, therefore, an object of the present invention to provide adata transmitting/receiving apparatus and method for improving systemperformance in a mobile communication system.

[0038] It is another object of the present invention to provide a datatransmitting/receiving apparatus and method for increasing reliabilityin a mobile communication system.

[0039] It is also another object of the present invention to provide adata transmitting/receiving apparatus and method for enabling a receiverto receive high-priority bits with a relatively high receptionprobability at an initial transmission and retransmissions in a mobilecommunication system.

[0040] It is a further object of the present invention to provide a datatransmitting/receiving apparatus and method for creating a synergy ofbenefits by combining SMP with HARQ (Hybrid Automatic Repeat Request).

[0041] It is still another object of the present invention to provide adata transmitting/receiving apparatus and method in which systematicbits are always mapped to a high-reliability part at an initialtransmission and a plurality of retransmissions.

[0042] It is also still another object of the present invention toprovide a data transmitting/receiving apparatus and method for averagingthe reliabilities of systematic bits at an initial transmission and aplurality of retransmissions.

[0043] It is yet another object of the present invention to provide adata transmitting/receiving apparatus and method for averaging thereliabilities of coded bits differently depending on whether the codedbits are systematic bits or parity bits such that the averagereliability of the systematic bits is higher than that of the paritybits.

[0044] To achieve the above and other objects, according to one aspectof the present invention, a transmitter has a plurality ofconstellations having exchanged high-reliability and low-reliability bitpositions for bit-symbol mapping in a predetermined modulation scheme atan initial transmission and retransmissions and selects one of theconstellations according to an initial transmission or the sequencenumber of a retransmission. The transmitter separately outputstransmission data as high-priority bits and low-priority bits, andexchanges the position of the high-priority bits with the position ofthe low-priority bits so that the high-priority bits are mapped to thehigh-reliability bit position and the low-priority bits are mapped tothe low-reliability bit position.

[0045] According to another aspect of the present invention, in atransmitter that has a plurality of constellations with exchangedhigh-reliability and low-reliability bit positions for bit-symbolmapping in a predetermined modulation scheme at an initial transmissionand retransmissions and selects one of the constellations according toan initial transmission or the sequence number of a retransmission, achannel encoder separately outputs transmission data as high-prioritybits and low-priority bits, a first interleaver interleaves thehigh-priority bits, a second interleaver interleaves the low-prioritybits, a PSC converts the outputs of the first and second interleavers toone coded bit stream, a position exchange exchanges the positions of thehigh-priority bits and the low-priority bits received from the PSC, anda rearrangement controller compares a previous constellation and acurrent constellation and controls the position exchange to exchange bitpositions according to the comparison result.

[0046] According to a further aspect of the present invention, toreceive data produced by mapping high-priority bits to ahigh-reliability bit position and low-priority bits to a low-reliabilitybit position in symbols in a receiver, the high-priority bits and thelow-priority bits are demodulated from the high-reliability bit positionand the low-reliability bit position, respectively in the symbols.According to whether a transmitter has exchanged the bit positions, thepositions of the high-priority bits and the low-priority bits arecontrolled. If the transmitter has exchanged the bit positions, theposition of the high-priority bits is exchanged with that of thelow-priority bits in an original order. Then the high-priority bits andthe low-priority bits are combined with previously received same bits.

[0047] According to still another aspect of the present invention, toreceive data produced by mapping high-priority bits to ahigh-reliability bit position and low-priority bits to a low-reliabilitybit position in symbols, in a receiver, a demodulator demodulates thehigh-priority bits from the high-reliability bit position and thelow-priority bits from the low-reliability bit position in the symbols,a position exchange exchanges the position of the high-priority bitswith the position of the low-priority bits in an original order if atransmitter has exchanged the bit positions, a controller controls thepositions of the high-priority bits and the low-priority bits accordingto whether the transmitter has exchanged the bit positions, and acombiner combines the high-priority bits and the low-priority bits withpreviously received same bits.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

[0049]FIG. 1 illustrates a 8PSK signal constellation;

[0050]FIG. 2 illustrates a 16QAM signal constellation;

[0051]FIG. 3 illustrates a 64QAM signal constellation;

[0052]FIG. 4 is a block diagram of a transmitter in a typical HSDPAmobile communication system;

[0053]FIG. 5 is a block diagram of a transmitter in a conventional HSDPAmobile communication system supporting SMP;

[0054]FIG. 6 is a block diagram of a transmitter in a conventional HSDPAmobile communication system supporting CoRe;

[0055]FIGS. 7A to 7D illustrate signal constellations for symbol mappingin the transmitter illustrated in FIG. 6;

[0056]FIG. 8 is a block diagram of a transmitter in an HSDPA mobilecommunication system according to an embodiment of the presentinvention;

[0057]FIG. 9 is a block diagram of a receiver in the HSDPA mobilecommunication system according to the embodiment of the presentinvention;

[0058]FIG. 10 is a flowchart illustrating the operation of thetransmitter in the HSDPA mobile communication system according to theembodiment of the present invention; and

[0059]FIG. 11 illustrates graphs showing a comparison in performancebetween symbol mapping according to the present invention andconventional symbol mapping.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0060] A preferred embodiment of the present invention will be describedherein below with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail since they would obscure the invention inunnecessary detail.

[0061] CoRe discords with SMP. When SMP is used at an initialtransmission and CoRe is used at a retransmission, systematic bits(i.e., high-priority bits) are mapped to a high-reliability (H) part atthe initial transmission, and to a low-reliability (L) part at theretransmission. According to the present invention, the systematic bitsare always mapped to the high-reliability part by exchanging theposition of the systematic bits with the parity bits at theretransmission.

[0062] HARQ techniques include chase combining (CC), full incrementalredundancy (FIR), and partial incremental redundancy (PIR) according topuncturing patterns used for channel encoding. At initial transmissionand at retransmission, the same data is transmitted in CC, whereasdifferent data is transmitted in FIR and PIR. Only parity bits areretransmitted in FIR, and systematic bits and parity bits areretransmitted in PIR. Therefore, SMP is implemented in a differentmanner according to the HARQ techniques. In the presence of transmissiondata, systematic bits and parity bits are mapped to a high-reliabilitypart and a low-reliability part, respectively. On the other hand, in theabsence of transmission data, parity bits are separated and then mappedto a high-reliability part and a low-reliability part.

[0063]FIG. 8 is a block diagram of a transmitter in an HSDPA mobilecommunication system according to an embodiment of the presentinvention. Referring to FIG. 8, a CRC adder 820 adds CRC bits for errorcorrection to data received from a data source 810. A channel encoder830 encodes the CRC-attached data in a predetermined coding method suchas turbo coding or systematic convolutional coding, and outputssystematic bits S and parity bits P. Specifically, the channel encoder830 includes a plurality of constituent encoders for encoding input dataat a mother code rate and a puncturer for puncturing coded bits in apredetermined puncturing pattern. In incremental redundancy (IR), thechannel encoder 830 is provided with a plurality of puncturing patternsand selectively uses them at each retransmission. In PIR, for example, aplurality of puncturing patterns are used in which initially transmittedsystematic bits are reserved and parity bits are changed at eachre-transmission. In FIR, a plurality of patterns are used in whichsystematic bits are punctured and different parity bits are transmittedat each retransmission. Therefore, the channel encoder 830 outputssystematic bits and parity bits at a retransmission in PIR, while itoutputs only parity bits at a retransmission in FIR.

[0064] A distributor 835 distributes the systematic bits and the paritybits to a plurality of interleavers. If two interleavers 840 and 850 areused, the distributor 835 distributes them equally. When the channelencoder 830 uses a symmetrical code rate of ½, the distributor 835 feedsthe systematic bits to the first interleaver 840 and the parity bits tothe second interleaver 850. In this case, the distributor 835 isoptional in the present invention because the number of the systematicbits is equal to that of the parity bits at a code rate of ½ and theyare simply fed to the first and second interleavers 840 and 850,respectively. The distributor 835 is required only if the first andsecond interleavers 840 and 850 support a variable data length and anasymmetrical code rate. With a code rate of ¾, systematic bits andparity bits are produced at a ratio of 3:1 and the distributor 835provides part of the systematic bits to the first interleaver 840 andthe remaining systematic bits and the parity bits to the secondinterleaver 850. At a retransmission, the distributor 835 operates inthe same manner as at an initial transmission in CC and PIR. In FIR, thedistributor 835 separates the parity bits into two parity bit streamsand distributes them equally to the first and second interleavers 840and 850 at a retransmission.

[0065] At an initial transmission, the first interleaver 840 interleavessystematic bits received from the distributor 835 or the channel encoder830. In FIR, the first interleaver 840 interleaves parity bits receivedfrom the distributor 835 at a retransmission. The second interleaver 850interleaves parity bits received from the distributor 835 or the channelencoder 830.

[0066] A PSC 860 converts the parallel coded bits received from thefirst and second interleavers 840 and 850 to a serial bit stream. Whenthe first interleaver 840 interleaves high-priority coded bits and thesecond interleaver 840 interleaves low-priority bits, the PSC 860sequentially outputs the first interleaver output and the secondinterleaver output. Here, the ratio of the high-priority bits to thelow-priority bits output from the PSC 860 is determined according to thecode rate of the channel encoder 830 and the modulation scheme of amodulator 880 so that the high-priority bits, that is, the systematicbits, are mapped to a high-reliability part in a symbol. For example, in16QAM, two high-priority coded bits are output and then two low-prioritybits are output. Thus four coded bits are mapped to a modulation symbol.In 64QAM, three high-priority bits are output and then threelow-priority bits are output. Thus six coded bits are mapped to amodulation symbol.

[0067] A rearrangement controller 890 determines whether to exchange thesystematic bits with the parity bits output from the PSC 860 dependingon whether a receiver has requested a retransmission, that is, whetheran ACK or NACK signal has been received, and controls a positionexchanger 870 correspondingly.

[0068] At an initial transmission requiring no position exchange, theposition exchange 870 simply outputs the systematic bits and parity bitsreceived from the PSC 860 under the control of the rearrangementcontroller 890. At a retransmission requiring position exchange, theposition exchange 870 exchanges the positions of systematic bits andparity bits to be mapped to one symbol under the control of therearrangement controller 890. The thus-operated position exchange 870functions to map systematic bits and parity bits to be mapped to thesame reliability parts at a retransmission as at an initialtransmission. This enables coded bits to be mapped to modulation symbolsby SMP. That is, high-priority bits are mapped to a high-reliabilitypart and low-priority bits are mapped to a low-reliability part,irrespective of initial transmission or retransmission. The positionexchange 870 is applicable to any of CC, PIR, and FIR, which will bedescribed later in detail.

[0069] The modulator 880 maps the coded bits received from the positionexchange 870 to modulation symbols, sequentially using a plurality ofsignal constellations as illustrated in FIGS. 7A to 7D at an initialtransmission and at each retransmission under the control of therearrangement controller 890. The modulator 880 receives informationabout a constellation to be used for initial transmission orretransmission from the rearrangement controller 890.

[0070] Though not shown in FIG. 8, the transmitter may further include arate matcher for matching the rate of the coded bits received from thechannel encoder by repetition or puncturing.

[0071] Before describing the operation of the transmitter referring toFIG. 10, variables used in the flowchart of FIG. 10 are first definedbelow.

[0072] i: number of retransmission occurrences;

[0073] i_(max): the maximum number of retransmission occurrences;

[0074] k_(max): the total number of puncturing patterns;

[0075] PP_(k): a PIR puncturing pattern for an index k (k=0, . . .k_(max−1));

[0076] FP_(k): an FIR puncturing pattern for an index k (k=0, . . .k_(max−1));

[0077] j: an index that determines a constellation;

[0078] j_(max): the total number of constellations; and

[0079] M_(j): a constellation for an index j (=0, . . . j_(max−1))

[0080] Referring to FIG. 10, i and j are set to their initial values 0in step 1010 and it is determined whether a receiver has requested aretransmission in step 1012. In the case of initial transmission, step1014 to step 1026 are performed. On the other hand, in the case of aretransmission, step 1018 to step 1056 are performed. Here, SMP isapplied to an initial transmission and retransmission based on SMP iscarried out in a different manner according to CC, PIR, and FIR.

[0081] Initial Transmission

[0082] At the initial transmission, the CRC adder 820 adds CRC bits todata received from the data source 810 in step 1014. The channel encoder830 encodes the CRC-attached data at a predetermined mother code rate instep 1016. Systematic bits and parity bits output from the channelencoder 830 are punctured in a puncturing pattern P₀ for the initialtransmission and thus systematic bits and parity bits are outputaccording to a predetermined code rate in step 1018. The distributor 835distributes the systematic bits to the first interleaver 840 and theparity bits to the second interleaver 850 in step 1020 and the first andsecond interleavers 840 and 850 separately interleave the systematic andparity bits, in step 1022. In step 1026, the modulator 880 maps theinterleaved systematic and parity bits to modulation symbols using asignal constellation M0 for j=0 as illustrated in FIG. 7A. At theinitial transmission, step 1024 is omitted because no transmission hasbeen carried out before and there is no symbol structure to be comparedwith the initial transmission data. Step 1024 will be described indetail later in connection with data retransmission.

[0083] Retransmission in CC

[0084] In the case of retransmission, i is increased by 1 in step 1028and i is compared with i_(max) in step 1030. The variable i_(max) isused to limit the number of retransmissions. If i is equal to or greaterthan i_(max), the retransmission is terminated and the procedure returnsto step 1014. On the other hand, if i is less than i_(max),retransmission data is read from a buffer in step 1032. Though not shownin FIG. 8, the buffer is a memory for temporarily storing data in caseof retransmission before an ACK signal is received in a communicationsystem supporting data retransmission. In step 1034, it is determinedwhether CC is used as an HARQ technique. In CC, initially transmittedsystematic bits and parity bits are simply retransmitted. In IR, thesystematic bits and parity bits are changed for retransmission.

[0085] If the HARQ technique is CC, a constellation for symbol mappingat this retransmission is determined in step 1036. The index jindicating a constellation is determined by calculating modulo (i,j_(max)), Therefore, j is within a range from 0 to j_(max−1) and j_(max)constellations are cyclically used at retransmissions in CC. If j is 0,this means an initial transmission. As defined before, j_(max) is thetotal number of available constellations for symbol mapping. When theconstellations illustrated in FIGS. 7A to 7B are used, j_(max) is 4.Hence a different constellation is used for symbol mapping at eachretransmission in CC.

[0086] When the index j is determined in step 1036, step 1016 to 1022are performed in the same manner as for the initial transmission. Afterinterleaving in step 1022, the previous symbol structure is comparedwith a symbol structure for this retransmission. The symbol structure isequivalent to the relationship between coded bits and the reliability oftheir mapped part. For example, 16QAM has a symbol structure [H, H, L,L] with two first bits mapped to H determining a quadrant in aconstellation. However, a different symbol structure is used at aretransmission. For example, a symbol structure [L, L, H, H] can be usedat a first retransmission. Here, the last two coded bits mapped to Hdetermine a quadrant in a constellation. Thus, to map systematic bits toa high-priority part at a retransmission by SMP, the current symbolstructure must be compared with the previous symbol structure.

[0087] Referring to FIG. 7A, the first two bits of four coded bits foreach symbol are mapped to “H” indicating a quadrant. If the first twobits are “00”, they indicate the first quadrant, if the first two bitsare “10”, they indicate the second quadrant, if the first two bits are“11”, they indicate the third quadrant, and if the first two bits are“01”, they indicate the fourth quadrant. In the constellation for thefirst retransmission in 16QAM illustrated in FIG. 7B, the last two bitsof four coded bits for each modulation symbol are mapped to “H”determining a quadrant. That is, if the last two bits are “00”, theyindicate the first quadrant, if the last two bits are “10”, theyindicate the second quadrant, if the last two bits are “11”, theyindicate the third quadrant, and if the last two bits are “01”, theyindicate the fourth quadrant. The reliability patterns, that is, symbolstructures of the constellations illustrated in FIGS. 7A to 7D, vary inthe order of [H, H, L, L], [L, L, H, H], [L, L, H, H] and [H, H, L, L].The symbol structure for each odd-numbered retransmission is differentfrom the symbol structure for the initial transmission, and the symbolstructure for each even-numbered retransmission is identical to thesymbol structure for the initial transmission.

[0088] If the symbol structure for the previous transmission isdifferent from that of the constellation indicated by the index j forthe current retransmission in step 1024, the position exchange 870exchanges the positions of the previously transmitted systematic bitsand parity bits received from the PSC 860 in step 1038. For example, ifa symbol structure [H, H, L, L] is used for initial transmission andchanged to [L, L, H, H] at a first retransmission, the position exchange870 outputs two systematic bits after two parity bits, so the paritybits are mapped to “L” and the systematic bits to “H”. Then if thesymbol structure is changed to [H, H, L, L] at a second retransmission,the position exchange 870 outputs two parity bits after two systematicbits.

[0089] In step 1026, the modulator 880 maps the exchanged systematicbits and parity bits to modulation symbols in the jth constellationM_(j) according to its symbol structure. This, the two exchanged paritybits are mapped to “L” and the two exchanged systematic bits, to “H” inthe changed symbol structure.

[0090] Retransmission in PIR

[0091] If the HARQ technique is not CC in step 1034, which implies thatit is IR, an index k is determined to select a puncturing pattern bywhich systematic bits and parity bits different from initiallytransmitted systematic bits and parity bits can be obtained in step1040. The index k indicating a puncturing pattern is determined bycalculating modulo (i, k_(max)). Therefore, k is within a range from 0to k_(max−1) and k_(max) constellations are cyclically used atretransmissions in IR. As defined before, k_(max) is the total number ofavailable puncturing patterns for IR. IR includes PIR and FIR, andk_(max) puncturing patterns are provided for each of PIR and FIR. Thepuncturing patterns include the puncturing pattern P₀ for the initialtransmission.

[0092] When the index k is determined, it is determined whether k is 0in step 1042. If k is 0, this implies that an initial transmission and(k_(max)−1) retransmissions have been carried out. In IR, four to sixdifferent puncturing patterns are usually used. If k_(max) is 6, oneinitial transmission and five retransmissions occur with six puncturingpatterns, since i=6, k=0. When IR is used for constellationrearrangement in conjunction with SMP according to the presentinvention, retransmissions using all available puncturing patterns arecarried out by symbol mapping in the same constellation. In other words,a different constellation is used when the first puncturing pattern iscyclically selected again after all the puncturing patterns are used.

[0093] Therefore, when k=0, the index j is increased by 1 and j isupdated to modulo (j+1, j_(max)) in step 1046.

[0094] If k is not 0 or j is updated, the channel encoder 830 encodesretransmission data at a predetermined mother code rate in step 1044 andit is determined whether PIR is used as an HARQ technique in step 1048.In the case of PIR, the channel encoder 830 punctures the coded bitsincluding systematic bits and parity bits in a PIR puncturing patternPP_(k) corresponding to the index k in step 1050. Then the distributor835 distributes the systematic bits and the parity bits to the first andsecond interleavers 840 and 850 in step 1020 and the first and secondinterleavers 840 and 850 interleave the systematic and parity bits,separately in step 1022. The PSC 860 converts the parallel interleavedsystematic and parity bits to a serial bit stream. When a positionexchange is required in step 1024, the position exchange 870 exchangesthe positions of the systematic and parity bits in step 1038. On theother hand, if a position exchange is not required, the positionexchange 870 simply outputs the systematic and parity bits received fromthe PSC 860. Only if k=0 in step 1042, is the position exchange requiredin PIR because each time k is 0, a different constellation is used. Instep 1026, the modulator 880 maps the systematic and parity bitsreceived from the position exchange 870 to modulation symbols using asignal constellation M_(j).

[0095] To realize SMP-based signal rearrangement in PIR, bits encoded ata mother code rate are punctured in a kth puncturing pattern,interleaved, and then mapped to modulation symbols using a jthconstellation at a kth retransmission.

[0096] Retransmission in FIR

[0097] If the HARQ technique is not PIR in step 1048, which implies thatit is FIR, the channel encoder 830 punctures all the systematic bits andpart of the parity bits in a puncturing pattern FP_(k) corresponding tothe index k in step 1052. Then the distributor 835 distributes theparity bits to the first and second interleavers 840 and 850 in step1054 and the first and second interleavers 840 and 850 interleave theparity bits in step 1056. The PSC 860 converts the parallel interleavedparity bits to a serial bit stream. In FIR, the position exchange 870simply output the parity bits received from the PSC 860 without positionexchange. In step 1056, the modulator 880 maps the parity bits receivedfrom the position exchange 870 to modulation symbols using a signalconstellation M_(j).

[0098]FIG. 9 is a block diagram of a receiver in the HSDPA mobilecommunication system according to the embodiment of the presentinvention. Referring to FIG. 9, a demodulator 910 demodulates datareceived from the transmitter to coded bits in a demodulation methodcorresponding to the modulation scheme used in the modulator 880. Thedemodulator 910 uses the same constellation as used in the transmitterunder the control of a rearrangement controller 990. If the transmitterexchanges the positions of systematic bits and parity bits to map thesystematic bits to a high-reliability part, the receiver must exchangebit positions correspondingly. That is, the receiver must recover theoriginal bit order at a position exchange 920 under the control of acontroller 985.

[0099] A combiner 930 combines coded bits received from the positionexchange 920 with previously received sate data, on a bit-by-bit basis.When data retransmission is carried out by CC, the combiner 930 combinescoded bits on a bit-by-bit basis each time it receives them. In the caseof PIR, the combiner 930 combines systematic bits at each transmissionand combines parity bits in a predetermined period. In the case of FIR,the combiner 930 combines parity bits periodically because only paritybits are transmitted at each retransmission. The combining period is theperiod of repeating puncturing patterns used in the transmitter. Thecombiner output is separated according to priority, for separatedeinterleaving.

[0100] Then an SPC (Serial-to-Parallel) converter 940 converts a serialbit stream received from the combiner 930 to parallel streams. Forexample, if the modulator 880 employs 16QAM, the SPC 940 switches firsttwo bits for one symbol to a first deinterleaver 950 and the twofollowing bits to a second deinterleaver 960. If the modulation schemeis 64QAM, the SPC 940 switches the first three bits for one symbol tothe first deinterleaver 950 and the three following bits to the seconddeinterleaver 960. Meanwhile, if the transmitter uses interleaverssupporting an asymmetrical code rate and a variable length, the SPC 940must know the variable length so that it can output coded bits of thesize of the first interleaver 840 to the first deinterleaver 950 andoutput coded bits of the size of the second interleaver 850 to thesecond deinterleaver 960.

[0101] The first and second deinterleavers 950 and 960 deinterleave thecoded bits received from the SPC 940 in a deinterleaving methodcorresponding to the interleaving in the first and second interleavers840 and 850. The interleaving pattern is preset between the transmitterand the receiver. For example, the transmitter may notify the receiverof the interleaving pattern as system information before communication.When SMP is applied in the present invention, the first deinterleaver950 and the second deinterleaver receive the systematic bits and theparity bits and deinterleave them, separately.

[0102] A channel decoder 970 receives the deinterleaver outputs anddecodes systematic bits using parity bits for error correction in apredetermined decoding method corresponding to the coding in thetransmitter.

[0103] A CRC checker 980 checks CRC bits in the decoded bits anddetermines whether to request a retransmission of the data according tothe CRC check result. If the data has errors and its retransmission isrequested, an NACK signal is transmitted to the transmitter. On theother hand, if the data is normal and its retransmission is not needed,an ACK signal is transmitted to the transmitter and the next data isreceived.

[0104] As described above, high-priority coded bits (systematic bits)and low-priority coded bits (parity bits) are always respectively mappedto a high-reliability part and a low-reliability part in a symbolirrespective of initial transmission or retransmission. Therefore, whenCoRe is used for data retransmission, the reliabilities of thesystematic bits are averaged always in the high-reliability part and thereliabilities of the parity bits are averaged always in thelow-reliability part. As a result, the average reliability of thesystematic bits is higher than that of the parity bits.

[0105]FIG. 11 illustrates graphs showing a comparison in throughputamong a conventional retransmission scheme, CC, SMP and CoRe underdiscussion, and the priority-based discriminate reliability averagingmethod (SMP+CoRe) according to the present invention. While eachtechnique can be combined with an IR technique, it is used incombination with CC here.

[0106] Referring to FIG. 11, SMP has a 0.1 to 0.3 dB gain increase fromCC and CoRe has a 0 to 0.5 dB increase from CC. However, a combined useof SMP and CoRe according to the present invention brings a 0.3 to 2.3dB gain increase, which is a remarkable improvement.

[0107] While the embodiment of the present invention considers only thereliabilities of the four quadrants in a constellation when SMP isapplied, reliability differs in a plurality of symbols in each quadrant.Thus another embodiment can be contemplated by combining SMP with CoRefurther considering the reliabilities of the symbols.

[0108] To describe it in detail, common bits in the symbols of eachquadrant in a constellation have been defined as high-reliability (H)bits (i₁ and q₁ in FIGS. 2 and 3). Only if a symbol is received in awrong quadrant, the high-reliability bits will have errors. Therefore,they have a less error probability than low-reliability bits. However,reliability differs in the high-reliability bits. Referring to FIG. 2,since the four symbols in each quadrant initially have the same two bitsand the two high-reliability bits have errors when the symbols aretransmitted in a wrong quadrant, symbols near to the axes are lower inreliability than symbols far from the axes. Therefore, the four symbolscan be divided into three reliability regions. That is, a symbol near toboth axes has a low reliability, two symbols near to one of the axes andfar from the other axis have a medium reliability, and a symbol far fromboth axes has a high reliability.

[0109] When data retransmission does not occur, the probability oftransmitting all systematic bits in high reliability symbols even withSMP is only ¼. Since the systematic bits are mapped to a highreliability part, a sufficient gain is achieved. Nevertheless, it ismore important to achieve a high average reliability of the systematicbits. Therefore, coded bits are separately mapped to a high-reliabilitypart and mapped to a low reliability part according to their prioritylevels at an initial transmission and the high reliabilities and the lowreliabilities are separately averaged, resulting in different averagereliabilities according to the priority levels.

[0110] In accordance with the present invention as described above, acombined use of SMP and CoRe creates a synergy of benefits.High-priority bits are mapped to high-reliability bit positions whichare more robust against noise or other adverse environmental factors,and thus have a higher average reliability than low-priority bits atretransmissions. As a result, a much higher performance gain isachieved. As compared to existing systems, a frame error rate (FER) isdecreased and the overall system performance is improved irrespective ofwired or wireless communication, especially in the third generationwires communication system (IMT-2000).

[0111] While the invention has been shown and described with referenceto a certain preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A method of selectively transmitting data using one of a plurality of constellations having exchanged high-reliability and low-reliability bit positions for bit-symbol mapping in a predetermined modulation scheme at an initial transmission and retransmissions, the constellation being selected according to an initial transmission or the sequence number of a retransmission in a mobile communication system, the method comprising the steps of: separately outputting transmission data as high-priority bits and low-priority bits; and exchanging the position of the high-priority bits with the position of the low-priority bits so that the high-priority bits are mapped to the high-reliability bit position and the low-priority bits are mapped to the low-reliability bit position.
 2. The method of claim 1, further comprising the steps of: generating systematic bits and parity bits by encoding the transmission data at a predetermined mother code rate; and puncturing the systematic bits and parity bits in a puncturing pattern determined according to a retransmission scheme and outputting the punctured systematic bits as the high-priority bits and the punctured parity bits as the low-priority bits.
 3. The method of claim 2, wherein if the retransmission scheme is CC (Chase Combining), the constellation is selected according to an index obtained by modulo (the sequence number of a retransmission+1, the total number of the constellations).
 4. The method of claim 2, wherein if the retransmission scheme is an IR (Incremental Redundancy) and the constellations are cyclically repeated for use, the constellation is selected according to an index obtained by modulo (a previous index+1, the total number of the constellations).
 5. The method of claim 2, wherein if the retransmission scheme is CC, the same puncturing pattern is used for an initial transmission and retransmissions.
 6. The method of claim 2, wherein if the retransmission scheme is an IR, the puncturing pattern is determined according to an index obtained by modulo (the sequence number of a retransmission+1, the total number of the puncturing patterns).
 7. The method of claim 6, further comprising the step of dividing the punctured parity bits into two groups and separately interleaving the two parity groups if the IR is FIR (Full Incremental Redundancy).
 8. An apparatus for selectively transmitting data using one of a plurality of constellations having exchanged high-reliability and low-reliability bit positions for bit-symbol mapping in a predetermined modulation scheme at an initial transmission and retransmissions, the constellation being selected according to an initial transmission or the sequence number of a retransmission in a mobile communication system, the apparatus comprising: a channel encoder for separately outputting transmission data as high-priority bits and low-priority bits; a first interleaver for interleaving the high-priority bits; a second interleaver for interleaving the low-priority bits; a parallel to serial converter (PSC) for converting the outputs of the first and second interleavers to one coded bit stream; a position exchange for exchanging the positions of the high-priority bits and the low-priority bits received from the PSC; and a rearrangement controller for comparing a previous constellation and a current constellation and controlling the position exchange to exchange bit positions according to the comparison result.
 9. The apparatus of claim 8, wherein the channel encoder generates systematic bits and parity bits by encoding the transmission data at a predetermined mother code rate, punctures the systematic bits and parity bits in a puncturing pattern determined according to a retransmission scheme, and outputs the punctured systematic bits as the high-priority bits and the punctured parity bits as the low-priority bits.
 10. The apparatus of claim 9, wherein if the retransmission scheme is CC (Chase Combining), the constellation is selected according to an index obtained by modulo (the sequence number of a retransmission+1, the total number of the constellations).
 11. The apparatus of claim 9, wherein if the retransmission scheme is an IR (Incremental Redundancy) and the-constellations are cyclically repeated for use, the constellation is selected according to an index obtained by modulo (a previous index+1, the total number of the constellations).
 12. The apparatus of claim 9, wherein if the retransmission scheme is CC, the same puncturing pattern is used for an initial transmission and retransmissions.
 13. The apparatus of claim 9, wherein if the retransmission scheme is an IR, the puncturing pattern is determined according to an index obtained by modulo (the sequence number of a retransmission+1, the total number of the puncturing patterns).
 14. The apparatus of claim 13, further comprising a distributor for distributing punctured parity bits to the first and second interleavers, if the IR is FIR (Full Incremental Redundancy).
 15. A method of transmitting data using a predetermined code rate and a predetermined modulation scheme in a mobile communication system, comprising the steps of: generating high-priority bits and low-priority bits by channel encoding transmission data and mapping the high-priority bits to a high-reliability bit position and the low-priority bits to a low-reliability bit position in symbols at an initial transmission; and selecting one of a plurality of puncturing patterns for channel encoding and selecting one of a plurality of constellations where the high-reliability bit position is exchanged with the low-reliability bit position, for symbol mapping upon request for a retransmission from a receiver, puncturing the high-priority bits and the low-priority bits, exchanging the position of the punctured high-priority bits with the position of the punctured low-priority bits, and mapping the high-priority bits to the high-reliability bit position and the low-priority bits to the low-reliability bit position in symbols at a retransmission.
 16. The method of claim 15, wherein the channel encoding comprises the steps of: generating systematic bits and parity bits by encoding the transmission data at a predetermined mother code rate; and puncturing the systematic bits and parity bits in a puncturing pattern determined according to a retransmission scheme and outputting the punctured systematic bits as the high-priority bits and the punctured parity bits as the low-priority bits.
 17. The method of claim 15, wherein if the retransmission scheme is CC (Chase Combining), the constellation is selected according to an index obtained by modulo (the sequence number of a retransmission+1, the total number of the constellations).
 18. The method of claim 15, wherein if the retransmission scheme is an IR (Incremental Redundancy) and the constellations are cyclically repeated for use, the constellation is selected according to an index obtained by modulo (a previous index+1, the total number of the constellations).
 19. The method of claim 16, wherein if the retransmission scheme is CC, the same puncturing pattern is used for an initial transmission and retransmissions.
 20. The method of claim 16, wherein if the retransmission scheme is an IR, the puncturing pattern is determined according to an index obtained by modulo (the sequence number of a retransmission+1, the total number of the puncturing patterns).
 21. The method of claim 20, further comprising the step of dividing the punctured parity bits into two groups and separately interleaving the two parity groups if the IR is FIR (Full Incremental Redundancy).
 22. A method of receiving data produced by mapping high-priority bits to a high-reliability bit position and low-priority bits to a low-reliability bit position in symbols, in a receiver in a mobile communication system, comprising the steps of: demodulating the high-priority bits from the high-reliability bit position and the low-priority bits from the low-reliability bit position in the symbols; controlling the positions of the high-priority bits and the low-priority bits according to whether a transmitter has exchanged the bit positions; exchanging the position of the high-priority bits with the position of the low-priority bits in an original order if the transmitter has exchanged the bit positions; and combining the high-priority bits and the low-priority bits with previously received same bits.
 23. An apparatus for receiving data produced by mapping high-priority bits to a high-reliability bit position and low-priority bits to a low-reliability bit position in symbols, in a receiver in a mobile communication system, comprising: a demodulator for demodulating the high-priority bits from the high-reliability bit position and the low-priority bits from the low-reliability bit position in the symbols; a position exchange for exchanging the position of the high-priority bits with the position of the low-priority bits in an original order if a transmitter has exchanged the bit positions; a controller for controlling the positions of the high-priority bits and the low-priority bits according to whether the transmitter has exchanged the bit positions; and a combiner for combining the high-priority bits and the low-priority bits with previously received same bits. 